The present invention relates to a novel physiologically active substance and a process for producing the same. New physiologically active substances useful as medicaments or their intermediates are always in demand. To this end, it has been found that a new physiologically active substance is produced in the culture liquor of a microorganism belonging to the genus Actinomadura. When isolated and purified, the substance exhibits marked hypotensive activity. The substance has been named K-4 and its properties, a process for producing the same and a pharmaceutical composition containing the same are described hereinafter.